Do it Yourself?

The inverter coolant isn't that hard to do; but the engine coolant is relatively difficult due to the presence of the coolant heat recovery canister in the LH fender. You will find that it is not easy to purge air out of the engine coolant loop due to the canister - but it can be done given sufficient persistence and time. Note that the change interval for the factory-fill SLLC is 100K miles.

I don't have the Haynes manual but in case you need more help I suggest you download official Toyota repair manual info from techinfo.toyota.com which is a subscription website.

My guess is that the Toyota dealer price to replace the rear brakes and flush the coolant for both engine and inverter will be more like $500-600.

 

the brake pads are no different than other toyota small car rear drum brakes. so long as you don't open the brake lines that's no problem to diy. the dealer will probably charge 180-250 for parts and labor, which might include resurfacing drums.

coolant exchange is cheaper, since you can't feasibly flush the coolant. maybe 30-90 for labor plus the cost of coolant, per loop. it's a pain to diy, but if you leave the chs tank out of the equation (ie, clamp off the lines running to and from) it's less of a pain in the nice person.

your call as to what cost is worth it vs your time.